Growing up in the Brazilian city of Lagarto, Costa has since proclaimed "the street was my school."

Denied the pampering most teenage stars receive at club's academies these days, he grew up thinking aggression in football was fine.

"I was used to seeing players elbowing each other in the face and thought it was the norm," he once said. "Nobody ever told me otherwise."

Despite the fighting, Costa had a talent and, after moving to Sao Paulo and playing for Barcelona Esportivo Capel, an associate of that wily old agent Jorge Mendes spotted an 18-year-old Costa and packed him off on a plane to Portuguese club Braga.

(Image: Getty)

By 2007, Atletico had seen enough of him at Braga to make a move for him - but his performances over the last 18 months have been a long time in the making.

Loan spells with Celta Vigo, Albacete and Real Valladolid, mixed in with brief flirtations with Los Rojiblancos' first team, didn't quite manage to cultivate him into the forward he is today.

It was another loan spell, this time at Real Vallecano, his subsequent return to Atletico Madrid and the appointment of Diego Simeone - who has purred “the sky is the limit for Diego Costa” - which have propelled him into the top bracket of strikers in Europe.

And during the last year, notably since the departure of Radamel Falcao to Monaco, Costa has become one of the symbols of an Atletico team which were among the best in Europe last season.

His performances have left not just clubs, but countries fighting over him too.

Feeling unloved by his homeland, and crediting Spain with maturing him as a player, Costa took the decision to play for La Roja, rather than Brazil.

At the time Barcelona's Andres Iniesta praised his new international colleague for "showing almost unbeatable performance levels,” while Dani Alves loathed his defection. “He would have been important for Brazil,” the full-back claimed.

Unfortunately that decision didn't work out for him at the World Cup this summer.

Chelsea will hope he can be their new Didier Drogba, filling a void which has been glaringly absent since the Ivorian left the club, although Costa is far from a carbon copy.

One thing he will provide is an ability to constantly occupy defenders.

A common image in La Liga last season was him bamboozling through the middle of the pitch with up to four players clinging to his back, the ball somehow still stuck to his feet.

He'll also promise goals, in theory. Last season he scored 27 in the Spanish top flight and eight more in his debut Champions League season - fans at Stamford Bridge would settle for a similar return.

There are still concerns over Costa though, notably his discipline, but also his ability.

Geoffrey Kondogbia accused him of racism in the past, he's been sent off for pushing in Europe, he spits, he dives and his wars with Sergio Ramos and Pepe were regularly blockbuster viewing in Madrid derbies.

However, while he's still not an entirely likeable player for opposing fans, which is often a good thing, his act has cleaned up slightly as his performances have improved.

Perhaps anger will get the better of him at some point during the season, but Mourinho, as Simeone has largely done, should be able to keep him in check.

With regards to his ability, it's been suggested he may have enjoyed nothing more than a good season.

Towards the end of a long campaign, which saw Costa make 51 appearances for Atleti, his form did tail off slightly - although he was plagued with an on-going injury problem at this point - and it is possible, if unlikely, last season's feats were a fluke.

And despite his recent goal scoring record, you wouldn't be rushing to put your mortgage on his scoring a one-on-one.

Regardless of whether Mourinho sticks with a 4-2-3-1 formation, or changes to 4-3-3, Costa has the character, strength and confidence to lead the line - something nobody could do for the club last season.

Strictly based on last season, there are few better men than Costa to play Chelsea’s central striker role.